The present invention relates to a semiconductor device having cavities between metal interconnections and a method for fabricating the same.
With recent remarkable progress in semiconductor process technology, finer semiconductor elements and metal interconnections with higher integration have been pursued. With this trend toward finer size and higher integration, signal delay at metal interconnections has come to greatly influence the operation speed of semiconductor integrated circuinsorder to minimize signal delay at metal interconnections, proposed are methods for reducing the relative dielectric constant of an insulating film deposited between metal interconnections by forming cavities (xcex5=1.0) in the insulating film or by using an organic film as the insulating film, as described in Japanese Laid-Open Patent Publication No. 10-233448.
Conventional semiconductor devices adopting the above methods can reduce the relative dielectric constant to some extent. However, with further achievement of finer semiconductor elements and metal interconnections with higher integration, the distance between adjacent metal interconnections is further shortened. This increases the capacitance between metal interconnections and thus inevitably causes signal delay at metal interconnections.
To avoid the above trouble, the present inventors conceived a method for reducing the relative dielectric constant of an insulating film between metal interconnections, where an insulating film made of a fluorine-containing organic film is deposited between metal interconnections using a perfluorocarbon gas such as CF4 gas, C2F6 gas, C3F8 gas, and C4F8 gas and also cavities are formed in the insulating film.
However, the inventors noticed that the perfluorocarbon gases described above have a large global warming potential (GWP100) and thus have a possibility of causing global warming due to the greenhouse effect if used in high volume in an industrial scale.
In addition, the fluorine-containing organic film deposited using any of the above perfluorocarbon gases is poor in adhesion to an underlying film due to existence of a number of free fluorine atoms in the organic film.
Moreover, the fluorine-containing organic film deposited using any of the above perfluorocarbon gases lack denseness due to existence of a number of free fluorine atoms in the film, and thus poor in mechanical strength, heat resistance, and chemical resistance.
In view of the above, the object of the present invention is allowing a fluorine-containing organic film that is superior in adhesion to an underlying film and denseness and has cavities between metal interconnections to be deposited between metal interconnections without a possibility of causing global warming.
In order to attain the above object, the first method for fabricating a semiconductor device of the present invention includes the steps of: forming a plurality of metal interconnections on a semiconductor substrate; and depositing a first fluorine-containing organic film between the plurality of metal interconnections and on top surfaces of the metal interconnections by holding the semiconductor substrate on a sample stage in a reactor chamber of a plasma processing apparatus and introducing a material gas containing C5F8, C3F6, or C4F6 as a main component into the reactor chamber, the first fluorine-containing organic film having cavities between the metal interconnections.
According to the method for fabricating a semiconductor device of the present invention, the first fluorine-containing organic film is deposited using the material gas containing C5F8, C3F6, or C4F6 that has a short atmospheric life and a small GWP100 as a main component. Therefore, global warming is less easily caused even when the device is mass-produced in an industrial scale.
In addition, all of C5F8 gas, C3F6 gas, and C4F6 gas have carbon-to-carbon double bonds. During film formation, carbon-to-carbon double bonds are dissociated, and resultant carbon atoms are bound with free fluorine atoms. This reduces the number of free fluorine atoms in the first fluorine-containing organic film. The resultant deposited first fluorine-containing organic film is dense and improves in adhesion to an underlying film.
Moreover, since the first fluorine-containing organic film has cavities between the metal interconnections, the relative dielectric constant between the metal interconnections is lowered. This reduces signal delay at the metal interconnections.
Preferably, the method for fabricating a semiconductor device of the present invention further includes the step of: depositing a second fluorine-containing organic film having no cavities on the first fluorine-containing organic film by introducing a material gas containing C5F8, C3F6, or C4F6 as a main component into the reactor chamber.
The first fluorine-containing organic film that has cavities tends to be poor in mechanical strength. However, by depositing the second fluorine-containing organic film having no cavities on the first fluorine-containing organic film, the second fluorine-containing organic film compensates the poor mechanical strength of the first fluorine-containing organic film. Thus, compatibility between reduction in relative dielectric constant and securement of mechanical strength is attained in the interlayer insulating film composed of the first and second fluorine-containing organic films.
In the case of including the step of depositing a second fluorine-containing organic film having no cavities on the first fluorine-containing organic film, the step of depositing a first fluorine-containing organic film preferably includes the step of applying no bias voltage or applying a relatively low bias voltage to the sample stage, and the step of depositing a second fluorine-containing organic film preferably includes the step of applying a relatively high bias voltage to the sample stage.
By adopting the above steps, it is possible to form cavities in the first fluorine-containing organic film while forming no cavities in the second fluorine-containing organic film, using the same material gas.
In the case of including the step of depositing a second fluorine-containing organic film, also, a scavenger gas for scavenging fluorine atoms is preferably mixed in the material gas used in the step of depositing a second fluorine-containing organic film.
By mixing a scavenger gas, the number of fluorine ions in the plasma decreases. Therefore, in the second fluorine-containing organic film, the proportion of fluorine atoms decreases while the proportion of carbon atoms increases. The resultant second fluorine-containing organic film is superior in mechanical strength although being high in relative dielectric constant.
In the above case, the scavenger gas is preferably CO gas. This ensures scavenging of fluorine atoms generated when C5F8, C2F6, or C4F6 is changed to plasma.
In the case of including the step of depositing a second fluorine-containing organic film, preferably, the method further includes the step of densifying the second fluorine-containing organic film by exposing the second fluorine-containing organic film to plasma of a rare gas in the reactor chamber. By this step, the second fluorine-containing organic film becomes dense, and thus improves in mechanical strength, heat resistance, and chemical resistance.
In the above case, the rare gas is preferably argon gas. The reason is as follows.
Argon gas is often added to a material gas for film formation since the deposition rate improves by adding argon gas to the material gas. Therefore, by using plasma of argon gas for densifying, the same rare gas can be used for both the film formation process and the densifying process. This makes easy to perform the film formation process and the densifying process sequentially in the same reactor chamber.
In the case of densifying the second fluorine-containing organic film, the second fluorine-containing organic film is preferably exposed to the plasma of a rare gas in a state where the semiconductor substrate has moved toward a plasma generation region in the reactor chamber. This facilitates densifying of the fluorine-containing organic film.
In the method for fabricating a semiconductor device of the present invention, the step of depositing a first fluorine-containing organic film preferably includes the step of controlling a residence time of the gas used as a main component of the material gas depending on the kind of the gas so that cavities are formed.
The above process ensures deposition of the first fluorine-containing organic film having cavities between the metal interconnections.
The semiconductor device of the present invention includes: a plurality of metal interconnections formed on a semiconductor substrate; a first fluorine-containing organic film having cavities deposited between the plurality of metal interconnections and on top surfaces of the metal interconnections; and a second fluorine-containing organic film having no cavities deposited on the first fluorine-containing organic film.
According to the semiconductor device of the present invention, the second fluorine-containing organic film having no cavities deposited on the first fluorine-containing organic film compensates the poor mechanical strength of the first fluorine-containing organic film. Thus, compatibility between reduction in relative dielectric constant and securement of mechanical strength is attained in the interlayer insulating film composed of the first and second fluorine-containing organic films.